EPF (Early Pregnancy Factor) is a protein that during pregnancy occurs in the blood or urine or in biochemical derivatives of blood or urine of pregnant women. In addition to its presence during pregnancy, EPF also occurs in these fluids when gonadal tumors exist (testicular or ovarian tumors) [Aust. J. Biol. Sci. 37 (1984) 393-407]. [Fertility and Sterility 35 (1981) 397-402]
EPF binds on lymphocytes and can be detected in the rosette inhibition test. The test is based on the fact that EPF intensifies the inhibition of the active rosette formation between lymphocytes and heterologous erythrocytes by antilymphocyte serum [Proc R. Soc. London Ser. B. 193 (1976) 413-149]. In the rosette inhibition test, EPF can be detected in the serum of pregnant women already within 24 hours after conception (union of ovum and sperm) and 2-3 days later also in the urine of these women. In the case of in vitro fertilization a successful embryo transfer is indicated by the occurrence of EPF about 3 days after the transfer (Ann. N.Y. Acad. Sci. 442:420-8, 1985).
Therefore, with the aid of EPF diagnostics, a pregnancy can be detected at a very early moment (1-5 days after conception). However, the rosette inhibition test is labor-and time-consuming; moreover, it is subject to a high error rate. Even a positive pregnancy is often detected only after repeated tests. On the other hand, to rule out a pregnancy, several repetitions of the test are always necessary.
Therefore there is a great interest in a simple and reliable process for early detection of a pregnancy based on the occurrence of EPF.